Blood pressure and heart rate have long been recognized as indicators of the general physical well-being of a patient. Both blood pressure and heart rate are monitored in nearly all medical procedures, from a general physical examination to extensive surgery. Depending upon the condition of the subject and the need for accuracy, various approaches are used, particularly for measuring blood pressure.
For example, the most common method of measuring blood pressure in human subjects is with a stethoscope and sphygmomanometer, in which a nurse or other member of the medical staff inflates the cuff until the brachial artery is occluded and then, while deflating the cuff, listens with the stethoscope for the first Korotkoff sounds in the artery. When the first Korotkoff sounds are heard, the manometer reading is taken as an indication of systolic pressure. Diastolic pressure is indicated by further deflation of the cuff until the Korotkoff sounds indicate, to the nurse, that the vessel is no longer occluded, with the manometer providing the pressure indication.
As those skilled in the art will appreciate, the accuracy of the stethoscope and sphygmamonometer method depends upon the skill of the technician, and also depends on the technician's hearing. The result is that this approach is unreliable for situations requiring high repeatability and accuracy, although the sphymomanometer approach does provide a general indication of blood pressure, and has the advantage of being non-invasive.
The pitfalls of the stethoscope and sphygmomanometer technique are well recognized by the medical profession, and this approach is not used in many surgical contexts where accuracy is important, as in coronary care. In these demanding applications, the more common method of monitoring blood pressure is the intra-arterial catheter. An intra-arterial catheter, while providing improved accuracy, has the obvious drawback of requiring surgical implantation; i.e.--an invasive approach. Thus there has not been, prior to the present invention, a suitable non-invasive technique for monitoring blood pressure and related characteristics which provides satisfactory accuracy and repeatability to be useful in demanding surgical contexts.
In addition, none of the non-invasive devices which has existed previously could, automatically, interpret the signals provided by a transducer to provide indications of heart rate, diastolic and systolic pressures, and other characteristics to a high degree of repeatability.